The encyclopedia · Software & IT · Technical decision · 2012-2021
Google's QUIC moved the transport onto UDP and built TLS in, and it became HTTP/3
QUIC ran a multiplexed, encrypted transport over UDP, and the web adopted it as HTTP/3.
the move
TCP had served the web for decades, but its problems were baked into the operating system and middleboxes: head-of-line blocking, where one lost packet stalls everyone behind it on that connection, and a multi-roundtrip handshake. Fixing TCP means upgrading every kernel and network device.
Google's QUIC runs its own reliability and stream multiplexing on top of UDP, so no OS-wide TCP change is needed. It bundles TLS 1.3 into the same handshake, reducing setup to about one round trip, and ties the connection to a connection id rather than an IP, so it survives switching from Wi-Fi to cellular.
The single choice that made it practical was working above UDP. Google shipped it in Chrome and its own servers, proved the latency wins, then handed it to the IETF, which standardized it as the transport for HTTP/3.
why it works
- Because QUIC sits on UDP, Google could deploy it inside its own browser and servers without waiting for any kernel or carrier upgrade.
- Multiplexed streams mean one congested stream no longer blocks an entire connection's other streams, fixing TCP head-of-line.
- Combining TLS 1.3 into the handshake cuts connection setup from multiple round trips to about one.
- Connection migration lets a session survive network changes, which is vital on mobile, and keeps it identified even when the IP moves.
what transfers
If the incumbent transport is locked behind kernel and carrier upgrades you do not control, move your transport to the datagram layer where you can ship it in your own client.
what came after
QUIC was standardized as RFC 9000 in May 2021 with HTTP/3 defined in RFC 9114, and it is now enabled by default in every major browser. Cloud providers and CDNs support it, and it particularly helps mobile and lossy networks. Tuning this UDP-based transport is harder than TCP, which remains a real operational cost.
references
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